These stats show what would have to happen for Donald Trump to beat Hillary Clinton

People who study political polling are all agreed: There is
no way that Donald Trump can beat Hillary Clinton and
become US president this year. It's simply not going to happen.

And yet ... never say never.

Some people have been passing around this chart of the 1980
election, which shows President Carter polling 29 points ahead of
Ronald Reagan at the beginning of the year. He was just a
celebrity, not a serious politician, after all:

Gallup

Of course, as the chart shows, Reagan went on to win, realigning
American politics in favour of the Republicans for a generation.
(And, it should be said,
Gallup's polling was not as sophisticated as it is today.)

The implication is that the same scenario might repeat itself:
The media and the pollsters are underestimating Trump's appeal.
After he has won the GOP nomination he somehow steadily gains
ground by tacking toward the political centre. Clinton puts in an
uninspiring performance. And Trump wins by a narrow margin in
November, the theory goes.

Currently, the polls show that is not likely to happen.
RealClearPolitics has a nice chart showing polls for a
Clinton-Trump matchup:

Hillary is comfortably ahead, and always has been. There were two
points, in December 2015 and February 2016, at which Trump
apparently pulled within striking distance. In the December poll,
the pair were separated by less than a point — well inside the
margin of error.

Most people are writing off those two polls as outliers. They
appear as sudden deviations from the trend, and the following
polls showed no diminution of Clinton's lead. The University of
Virginia’s Center for Politics has
a great map of what that looks like in the electoral college
— a landslide for Clinton.

Nonetheless, there are several polls in that RCP series where the
difference between them is only three or four points. If these
two were any other candidates, jumping that gap would look doable
for the Republican.

It goes like this: If you're white and don't have a college
degree, and you lost your job or saw your wages cut because of
the globalisation of free trade, then you're angry at both the
Republicans and the Democrats right now. Both parties cheered the
free trade deals that gutted the good manufacturing jobs from the
North and Midwest of America, and
Trump has a staunch anti-NAFTA, anti-China position.
Gagnon writes:

The number of these voters who have been depressed, ignored,
dismissed, and outright ridiculed is tremendous. And there are a
lot of them in states like Pennsylvania, Ohio, Michigan, and
Wisconsin. A lot.

That means that these states -- particularly Pennsylvania and
Michigan -- which have been Republican targets for nearly thirty
years to no avail, have a very real possibility of flipping.

Having said that, FiveThirtyEight
has a nifty interactive graphic that lets you adjust levels
of support among the various demographic groups so that you can
plot various election scenarios. It uses the 2012 election, which
Obama won with 51.7% of the vote, as its baseline.

If you're a Trump supporter (or if you buy Gagnon's theory), then
try sliding the scale for "non-college educated white people"
from 62% Republican support in 2012 to 69% today. You get this:

A Trump victory in the electoral college with just 48.2% of the
vote

If you believe that under-educated whites are the key to the
election then Trump needs an increase of seven points in
Republican support among that group. That's a big leap, but not
impossible. That result also assumes all the other demographics
vote the same way as they did for Obama in 2012 — which isn't
likely.

Again, the likely result is that Trump is so offensive
to Democrats and moderate Republicans that he drives them to
vote for Hillary, or to not vote at all, thus handing Clinton the
White House.